Update example.md

animation/basic_tween/example.md

@@ -4,6 +4,7 @@ title: Tween animation
 brief: This example shows how to tween animate the position of a game object.
 author: Defold Foundation
 scripts: spaceship.script
+thumbnail: basic_tween.png
 ---
 
 ![tween](basic_tween.png)